The invention is based on a regulating device. In a known regulating device of this type the shaft must be loosened in the armature in order to adjust the center of rotation of the control element relative to the position of the annular slide and, after making the adjustment, must be re-fastened. This is not possible during operation, since the control element becomes inoperable once the shaft is loosened. However, it is desirable to have an accurate adjustment which can only be made during operation.